The present invention relates generally to a radio frequency antenna system and, more specifically, to an antenna system for use in a hand-held telecommunication device, such as a mobile terminal.
A general approach in two-way radio communication is to use a common antenna operatively connected to a transmitter and a receiver via a duplex filter or an antenna switch for transmitting and receiving signals, respectively. Alternatively, two antennas are used, each with a separate filter. One antenna is used for transmission and the other for reception. When only a single antenna is used for reception, the received signals could be severely degraded due to phase-interference fading caused by multipath.
It is known that the effects of fading in radio communications and broadcast can be reduced by the simultaneous use of two or more physically separate antennas. If one antenna is in deep fading, the other may be in a useful reception condition. This technique is commonly referred to as space diversity. When two or more reception antennas are placed apart from each other, preferably over a distance exceeding a quarter wavelength of the received signals, for reducing the effects of fading in order to enhance coverage probability or better quality of service, the signals received from different reception antennas can be combined in a suitable manner, such as maximal ratio combining.
In a mobile terminal where a separate transmission antenna and reception antenna are used for transmitting and receiving signals, the transmission antenna and the reception antenna are tuned to different frequencies in an FDD (frequency division duplex) mode. As such, the transmission antenna does not work well at reception frequencies. In order to combat signal degradations due to fading using the space diversity scheme, additional antennas are needed. The additional antennas and their associated hardware will increase the manufacturing cost of the mobile terminal.
It is advantageous and desirable to provide a method and system for realizing space diversity in a hand-held telecommunications device without substantially increasing the manufacturing cost.
In a TDMA (time-division multiple access) type of transmission, the reception and transmission of signals are not necessarily or always active at the same time. For example, in a normal GSM (global system for mobile communications) system, one frame is divided into eight slots. In a normal GSM call, only one transmission slot and one reception slot are used at different times. In a GPRS (general packet radio system) system, more slots come into use. The GPRS terminals are classified as Type 1 and Type 2. In type 1, the terminal operates either in the reception mode or in the transmission mode. In type 2, the terminal can simultaneously operate in the transmission mode and in the reception mode.
When a type 1 terminal is implemented with separate transmission and reception antennas, the transmission antenna is not in use at all times. According to the present invention, the transmission antenna can be used as another reception antenna in the space diversity scheme. As mentioned earlier, the transmission and reception in an FDD system are carried out at different frequencies, rendering the transmission antenna relatively ineffective at the reception frequencies. According to the present invention, the transmission antenna, which is optimally tuned for transmitting, can be tuned to the reception band at least part of the time when the transmission antenna is not used for transmission.
In the United States, for example, several systems are operating at the same frequency bandxe2x80x94e.g. PCS band, which is used for Personal Communication Systems or a second generation cellular system, operating partly on the IMT (International mobile telephony)-2000 band. Such systems are: TDMA, GSM, IS-95 (narrow-band code-division multiple access or CDMA) and the forthcoming wideband CDMA (WCDMA). For use in such a frequency band, a multiple mode terminal may have more than one radio frequency (RF) receiver path. In addition, the U.S. multi-mode terminal may also be operable at the cellular band or 800 band. At the cellular band TDMA, GSM, IS-95 systems can be operating at the same time. The GSM-850 antenna, which is optimally tuned to the GSM-850 band for transmission and reception when the terminal is used for the GSM-850 mode, can be tuned to the PCS band for space diversity reception when the terminal is used for any of the PCS systems.
Thus, according to the first aspect of the present invention, there is provided a radio frequency antenna system capable of operating in a transmission mode and a reception mode. The antenna system comprises:
a first antenna optimally tuned for receiving signals in a first frequency band;
a second antenna optimally tuned for transmitting signals in a second frequency band different from the first frequency band when the system is operating in the transmission mode; and
means, operatively connected to the second antenna, for tuning the second antenna to a third frequency band substantially equal to the first frequency band when the system is operating in the reception mode so that the second antenna also receives the signals in the first frequency band.
Preferably, the antenna system also comprises means, operatively connected to the first antenna and the second antenna when the system is operating in the reception mode, for combining the signals in the first frequency band received by the second antenna and the signals received by the first antenna. The combining of signals can be carried out in an analog fashion or a digital fashion.
According to the first aspect of the present invention, the first antenna is disposed apart from the second antenna by a distance substantially equal to or exceeding a quarter wavelength of the first frequency band.
According to the second aspect of the present invention, there is provided a method of transmitting and receiving radio frequency signals in a telecommunications device, the telecommunications device having
a first antenna optimally tuned for receiving signals in a first frequency band; and
a second antenna operable in a transmission mode and a reception mode, wherein the second antenna is optimally tuned for transmitting signals in a second frequency band different from the first frequency band when the second antenna is operating in the transmission mode. The method comprises the step of tuning the second antenna to a third frequency band substantially equal to the first frequency band when the second antenna is operating in the reception mode so that the second antenna also receives the signals in the first frequency band.
Preferably, the method further comprises the step of combining the signals in the first frequency received by the second antenna and the signals received by the first antenna.
According to the third aspect of the present invention, there is provided a radio receiver system operable in a first mode and a second mode, the system having a first subsystem and a second subsystem, wherein the first subsystem includes a first receiver and a first antenna capable of receiving signals in the first mode in a first frequency range for providing the received signals to the first receiver, and the second subsystem includes a second receiver and a second antenna capable of receiving signals in the second mode in a second frequency range different from the first frequency range for providing the received signals to the second receiver. The radio receiver system comprises:
a first means, operatively connected to the first antenna, for tuning the first antenna to a reception frequency in the second frequency range when the system is operating in the second mode, such that the first antenna also receives the signals in the second mode in the second frequency range; and
a second means, operatively connected to the first antenna and the second receiver, for routing the signals received by the first antenna in the second mode to the second receiver.
Advantageously, the radio receiver system further comprises:
a third means, operatively connected to the second antenna, for tuning the second antenna to a reception frequency in the first frequency range when the system is operating in the first mode, such that the second antenna also receives the signals in the first mode in the first frequency range; and
a fourth means, operatively connected to the second antenna and the first receiver, for routing the signals received by the second antenna in the first mode to the first receiver.
According to the fourth aspect of the present invention, there is provided a radio communication system including a first subsystem and a second subsystem, wherein the first subsystem includes a receiver operating at a first frequency range, and the second subsystem includes a transmitter operating at a second frequency range different from the first frequency range. The radio communication system comprises:
a first antenna operatively connected to the receiver and optimally tuned for receiving signals in the first frequency range and conveying the received signals to the receiver when the system is used for reception;
a second antenna operatively connected to the transmitter and optimally tuned to the second frequency for transmitting signals from the transmitter when the system is used for transmission;
a tuning mechanism, operatively connected to the second antenna for tuning the second antenna to a third frequency range substantially equal to the first frequency range when the system is used for reception, so that the second antenna also receives signals in the first frequency range; and
means, operatively connected to the second antenna and the receiver, for conveying signals in the first frequency range received by the second antenna to the receiver when the system is used for reception.
Advantageously, when the first subsystem is operable in a first mode and in a different second mode, and the receiver is operable in a first mode, the first subsystem further includes:
further receiver operable in the second mode, and
a switching means, operatively connected to the receiver, the further receiver and the first antenna for conveying the signals received by the first antenna to the receiver when the first subsystem is operating in a first mode, and for conveying the signals received for the second antenna to the further receiver when the first subsystem is operating in the second mode.
Advantageously, when the second subsystem is operable in the first mode and in the second ode and the transmitter is operable in the first mode, the second subsystem further includes:
a further transmitter operable in the second mode, and
a further switching means, operatively connected to the transmitter, the further transmitter and the second antenna, for conveying the signals received by the second antenna to the transmitter when the second subsystem is operating in the first mode, and conveying the signals received by the second antenna to the further transmitter when the second subs stem is operating in the second mode.
According to the fifth aspect of the present invention, there is provided a method of radio telecommunications in a telecommunications device operable in a first mode in a first frequency range and a second mode in a second frequency range different from the first frequency range, wherein the device includes:
a first antenna capable of receiving signals in the first frequency range and conveying the received signals in the first frequency range to a first receiver, when the device is operating in the first mode; and
a second antenna capable of receiving signals in the second frequency range and conveying the received signals in the second frequency range to a second receiver, when the device is operating in the second mode. The method comprises the steps of:
tuning the first antenna to a reception frequency in the second frequency range when the device is operating in the second mode, such that the first antenna also receives the signals is the second frequency range; and
providing the signals received in the second frequency range by the first antenna to the second receiver.
Advantageously, the method further comprises the steps of:
tuning the second antenna to a reception frequency in the first frequency range when the device is operating in the first mode, such that the second antenna also receives the signals the first frequency range; and
providing the signals received in the first frequency range by the second antenna to the first receiver.
The present invention will be apparent upon reading the description taken in conjunction with FIGS. 1a-5.